1. Field of the Invention
This invention relates to electrical power generation by moving magnets.
2. Description of the Related Art
Moving a magnet through a conductive coil induces an electromotive force that generates a current in the coil. If the magnet is moved back and forth in a reciprocating motion, the direction of current flow in the coil will be reversed for each successive traverse, yielding an AC current.
Several electrical generating systems have been developed that make use of reciprocating magnet movement through one or more coils. For example, in U.S. Pat. No. 4,260,901, wave motion in a body of water causes a float to move up and down, which in turn imparts a reciprocating motion to a magnet that travels between a pair of coils stationed at opposite ends of its path. In U.S. Pat. No. 5,347,186, a rare earth magnet and a coil are positioned to move back and forth relative to each other. The magnet can either be fixed and the coil moved up and down relative to the magnet, as by wave action, the coil fixed and the magnet moved relative to the coil as by pneumatic pressure, or the coil housing shaken or vibrated, as by being carried by a jogger, to cause a reciprocating motion of the magnet which moves with the coil. In FIG. 10A of this patent, a pair of magnets in polar opposition to each other are connected to opposite sides of the pendulum arm of a tilt buoy, with a respective coil located beyond each magnet when the buoy is vertical. In response to wave action tilting the buoy back and forth, the arm pivots relative to the buoy so that the magnets alternately enter and exit the opposed coils, generating electric currents in the coils as they do so. Each magnet moves through only one respective coil.
In U.S. Pat. No. 5,818,132, a moving magnet is confined to a bi-directional linear or near-linear motion through each of at least two mutually spaced coils for providing power in applications such as long-life flashlights, alarm systems, communication devices located at places where conventional electric power sources are unavailable, and for relatively high power repetitive forces such as the forces on the heel of a shoe during walking or running. FIG. 11B of this patent is similar to FIG. 10A of U.S. Pat. No. 5,347,186; the inventor of both patents is the same. In FIG. 15 of this patent, three moving magnets are suspended in a tube by polar opposition to both each other and to end magnets, with a number of coils spaced along the outside of the tube. Each of the coils has a pair of outputs which go to a circuit that combines the coil outputs to produce a net DC output. The magnets are not connected to each other, but are kept apart by their polar opposition.
In general, an electric signal is generated in response to a changing magnetic field within a coil (taken perpendicular to the coil axis). The traditional reciprocating magnet generator is inefficient because, as realized by the present inventors, the highest magnetic field gradient is located by the end of the magnet, with only a small or zero gradient at its middle, so significant electrical generation occurs in only a relatively small portion of the coil as the magnet passes through. Furthermore, the portion of the coil which experiences little or no magnetic field gradient at any given time still contributes to the coil""s overall ohmic loss. Thus, much of the energy that goes into moving the magnet relative to the coil fails to produce a useful electric output.
The present invention seeks to provide a new electrical generator system and method which allows a much greater portion of the moving magnet energy to be converted to electrical power. This is accomplished by constraining a plurality of spaced magnets to move together relative to at least one coil, and preferably a plurality of coils, so that alternating increasing and decreasing magnetic fields are established to generate electric signals in the coils.
In a particular embodiment equal numbers of magnets and coils, having substantially equal lengths and spacings along a common axis, are employed. If the magnets are oriented in magnetic opposition to each other and generate similar fields, the component of the fields parallel to the axis will cancel at locations between successive magnets, thereby producing large magnetic field differentials as the magnets move relative to the coils and a consequent high voltage output. The outputs from the individual coils can be combined to produce a net generator output.
The magnets can be arranged for various types of motion, such as a reciprocating linear movement. To provide an ultra low friction interface between the magnets and an associated support structure, a ferrofluid or other lubricant having a static coefficient of friction less than 0.01 and a viscosity less than 10 centipoise can be used.
The electrical generator can be used to power various types of operating systems, such as battery chargers, cellular telephones, environmental sensors, signal transmitters and flashlights. The operating systems can be battery operated, with the generator charging the battery, or they can be operated by the generator in real time.
These and other features and advantages of the invention will be apparent to those skilled in the art from the following detailed description of particular embodiments, taken together with the accompanying drawings.